Field of the Invention
The present invention relates to a drive apparatus that drives a light emitting device.
Description of the Related Art
A drive apparatus that drives a light emitting device such as a semiconductor laser is used in a printer or the like. Japanese Patent Laid-Open No. 2004-165444 discloses a semiconductor laser drive apparatus which has an APC (Automatic Power Control) function to obtain a predetermined light output. The semiconductor laser drive apparatus disclosed in Japanese Patent Laid-Open No. 2004-165444 includes a photodiode, an operational amplifier, an analog switch, a hold capacitor, a voltage-current converting circuit, a switch circuit, a variable resistance, and a reference potential generating circuit. The photodiode makes a current, which is proportional to the emitted light quantity of a laser diode, to flow to the variable resistance. This current is converted into a voltage by the variable resistance and supplied to the inverting input terminal of the operational amplifier. A reference potential is supplied from the reference potential generating circuit to the non-inverting input terminal of the operational amplifier. The output terminal of the operational amplifier is connected to one terminal of the analog switch, and the other terminal of the analog switch is connected to the voltage-current converting circuit. A hold capacitor is connected between the other terminal of the analog switch and a ground potential. The voltage-current converting circuit converts the input voltage into a drive current of the laser diode. The switch circuit performs switching in accordance with a DATA signal. The semiconductor laser drive apparatus performs, by the above-described arrangement, feedback control on the current to be supplied to the laser diode so that the voltage detected using the photodiode is equal to the reference potential.
When increasing a light quantity control range, a feedback loop operation for implementing an APC function can become unstable in a region where the response characteristics of the components of the feedback loop are bad. For example, the light quantity of light to be emitted by a light emitting device can have, in a specific region, a low response characteristic in a component such as a voltage-current converting circuit, and the delay of the feedback loop could increase. If this delay becomes too large, oscillation occurs.